1. Field of the Invention
The present invention generally relates to the field of drilling, and more particularly, relates to apparatus for penetrating, sampling, probing, and testing of a medium.
2. Description of Prior Art
Effective probing, drilling and coring apparatus find use in a great number of areas such as, for example, planetary exploration, military, medical operations, construction, police investigations, geology, archaeology sports (for example hiking and rock climbing) and other games.
Existing drilling techniques are limited by the need for high axial forces, large power consumption, as well as a need to operate from a heavy platform to drill in non-horizontal and/or hard surfaces. The life of coring bits is markedly reduced by the breakdown of the binder that holds abrasive material on a bit surface.
Accordingly, the capability of existing rotary corers has limited application in power and mass constrained environments. As an example, a typical rotary corer that produces 10 mm cores in hard rocks requires at least 20 to 30 watts of power. Such drilling rigs cannot be duty cycled continuously without a loss of efficiency. In addition, drill motors can demand as much as three to four times surge current upon startup then during continuous operation.
Conventional rotary corers that, for example, produce 10 mm diameter cores which may require about 100-N to 150-N or more of axial preload and during core initiation, drill walk can induce torques on the drilling platform that may exceed 30 Nm and tangential forces of 100-N. The drill chatter delivers a low frequency, for example 2-10 Hz, high force perturbations on a drilling platform which requires conventional coring applications to utilize very stable and massive platforms.
In hard rock formations, conventional rotary drillers and corers lose an advantage that they sometimes demonstrate in soft materials. In hard rocks, conventional drillers stop drilling by shearing and spoliation and become grinders. The grinding process is accompanied by at least a 300% increase in consumed energy per unit length of the core. In addition, because the grinding mechanism is determined by the compression failure of the rock, the teeth of the corers must be re-sharpened frequently. Accordingly, sharpness of the bits must be monitored otherwise the heat generation at the tip may increase by a factor of up to 10 times. This increase is accompanied by a concomitant drop in drilling efficiency and often causes burning or melting of the drill bit.
Non-traditional drilling technologies, such as for example, lasers, electron beams, microwaves, hydraulic jets, are typically competitive only in applications that are not power limited. Down-the-well energy required to remove a unit volume of rock for so called “modern” technologies is about the same as grinding and melting, that is, three to five times higher than for shear drilling. Unfortunately, for modern technologies, the ratio of down-the-well power delivered versus input power generation is below several percent versus 10 to 30 percent for conventional drills. Accordingly, many space or power limited applications simply do not have enough power to employ a non-traditional drilling technique.
Hammering drills and particularly the Ultrasonic/Sonic Driller/Corer (USDC) as shown in various embodiments in various earlier-filed U.S. patents and applications offer a solution capable of coring into a variety of rocks and soils using low power and low axial load. The USDC is based on an ultrasonic/sonic actuator mechanism. The advantages of this are attractive for potential future robotic missions to explore the planets and moons.
Experiments have shown that the penetration rate of the USDC can be improved by a factor of ten by rotating the drill bit. This supplements the hammering action and provides for faster drilling rates and greater penetration depth. However, the increased speed of drilling results in more cuttings and requires removal of the cuttings.
It would be greatly advantageous to provide hammer drilling with rotation of the bit, where the bit is independently rotated by a motor to remove large volumes of powdered cuttings, and to provide a backup drilling action in case of failure of either rotary or hammering mechanism. It would also be advantageous to provide a bit design with flutes on the surface to remove the powdered cuttings.